Mercury toxicity in livers of northern pike (Esox lucius) from Isle Royale, USA

Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Comparative Biochemistry and Physiology Part C: Toxicology & Pharmacology 147 (2008): 331-338, doi:10.1016/j.cbpc.2007.12.003.Many laboratory studies have documented that mercury can be toxic to fish, but it is largely unknown if mercury is toxic to fish in their natural environments. The objective of our study was to investigate the toxic effects of mercury on northern pike (Esox lucius) at Isle Royale, Michigan. In 124 northern pike from eight inland lakes, concentrations of total mercury in skin-on fillets ranged from 0.069 to 0.622 µg/g wet wt. Concentrations of total mercury in livers increased exponentially compared with concentrations in fillets, to a maximum of 3.1 µg/g wet wt. Methylmercury constituted a majority of the mercury in livers with total mercury concentrations <0.5 µg/g wet wt, but declined to 28-51% of the mercury in livers with total mercury concentrations >0.5 µg/g wet wt. Liver color (absorbance at 400 nm) varied among northern pike and was positively related to liver total mercury concentration. The pigment causing variation in liver color was identified as lipofuscin, which results from lipid peroxidation of membranous organelles. An analysis of covariance revealed lipofuscin accumulation was primarily associated with mercury exposure, and this association obscured any normal accumulation from aging. We also documented decreased lipid reserves in livers and poor condition factors of northern pike with high liver total mercury concentrations. Our results suggest (i) northern pike at Isle Royale are experiencing toxicity at concentrations of total mercury common for northern pike and other piscivorous fish elsewhere in North America and (ii) liver color may be useful for indicating mercury exposure and effects in northern pike at Isle Royale and possibly other aquatic ecosystems and other fish species.Financial support was provided by the U.S. Environmental Protection Agency STAR Graduate Fellowship Program to P.E.D

Index Files

Index File

Appendix A. Sample sites in Twelvemile Creek.

Sample sites in Twelvemile Creek

Appendix C. Targeted PCB analytes and methods for extraction and analysis of samples by GC-ECD.

Targeted PCB analytes and methods for extraction and analysis of samples by GC-ECD

Appendix B. Summary PCB, 15N, and 13C for stream and riparian food webs.

Summary PCB, 15N, and 13C for stream and riparian food webs

Female genomic response to mate information

Females should be choosier than males about prospective mates because of the high costs of inappropriate mating decisions. Both theoretical and empirical studies have identified factors likely to influence female mate choices. However, male–male social interactions also can affect mating decisions, because information about a potential mate can trigger changes in female reproductive physiology. We asked how social information about a preferred male influenced neural activity in females, using immediate early gene (IEG) expression as a proxy for brain activity. A gravid female cichlid fish (Astatotilapia burtoni) chose between two socially equivalent males and then saw fights between these two males in which her preferred male either won or lost. We measured IEG expression levels in several brain nuclei including those in the vertebrate social behavior network (SBN), a collection of brain nuclei known to be important in social behavior. When the female saw her preferred male win a fight, SBN nuclei associated with reproduction were activated, but when she saw her preferred male lose a fight, the lateral septum, a nucleus associated with anxiety, was activated instead. Thus social information alone, independent of actual social interactions, activates specific brain regions that differ significantly depending on what the female sees. In female brains, reproductive centers are activated when she chooses a winner, and anxiety-like response centers are activated when she chooses a loser. These experiments assessing the role of mate-choice information on the brain using a paradigm of successive presentations of mate information suggest ways to understand the consequences of social information on animals using IEG expression

The blue tit's song is an inconsistent signal of male condition.

Sexually selected traits are often hypothesized to signal male condition or quality, though empirical evidence is mixed, and a number of alternative models of sexual selection do not require condition dependence. We examined the relationship between various measures of condition and dawn songs in male blue tits (Cyanistes caeruleus). We detected 6 largely independent measures of variation (i.e., variables) in these songs. None of these variables were related to blue tits' ultraviolet--blue plumage, a demonstrated sexual signal, thus failing to support the redundant signal hypothesis. We found some evidence that the song variables we measured signaled male quality. There were correlations between body size and certain song traits, though neither male age nor male recapture in the subsequent breeding season (apparent local survival) predicted any song variation. We combined our results with published effect sizes comparing blue tit song with male quality variables using meta-analysis and found that a few song measures are correlates of male quality, though as in our field data, neither male age nor survival appeared related to song. Our relatively large sample sizes (>60), combined with our meta-analytical integration of 89 effect sizes, make the results regarding the signaling value of our measured components of blue tit song robust. These results demonstrate that 1) only certain aspects of signal variation may be condition dependent and 2) even when components of a sexual signal appear correlated with condition in some studies, these signal components may be unrelated or inconsistently related to a variety of condition indices. Copyright 2006.condition dependence; dawn song; meta-analysis; Parus caeruleus; survival; ultraviolet

How Songbird Females Sample Male Song: Communication Networks and Mate Choice

The behavioural decisions animals take directly influence their fitness andthus have a fundamental impact on evolutionary processes. In many animals,acoustic signals play an important role in social decisions with mate choice beingamong the most apparent ones. Male bird song has played a key role along this line, yet the understanding of how female birds use song to prospect, assess and choose mates in their natural environment is surprisingly limited. A main reason for this limited understanding is that it is very difficult to follow a female during her prospecting and decision process and quantify her experience with different males before she makes a final decision. Here we integrate insights from communication networks, male song traits and female prospecting behaviour to stimulate a more integrative approach on the role of signalling in behavioural and reproductive decisions